People with iron overload disorders are more susceptible to serious infections with Yersinia and other bacterial pathogens, yet how and why the course of infection differs in these individuals remains unclear. Mutations that predispose humans to one such iron overload disorder, hereditary hemochromatosis, are very common. One hereditary hemochromatosis-associated mutation in the High Iron Fe gene (Hfe-C282Y) is found in 10% of people of Northern European descent. People with hereditary hemochromatosis accumulate iron in their livers and other tissues, which can lead to increased oxidative stress and organ damage if left untreated. However, hereditary hemochromatosis is also associated with low macrophage iron and immune system defects. Several excellent mouse models of hereditary hemochromatosis exist that recapitulate many symptoms of the human disease. However, these models have been underutilized in terms of characterizing susceptibility to infection. We have identified a gene in the foodborne pathogen Yersinia pseudotuberculosis that controls expression of the type III secretion system (T3SS), a specialized apparatus required by all pathogenic Yersinia to cause disease. This gene has significant homology to the E. coli transcription factor IscR, whose activity is controlled by iron availability and oxidative stress, both of which are abnormal in hereditary hemochromatosis. We hypothesize that IscR is important for proper control of T3SS expression and virulence of Y. pseudotuberculosis and the related pathogen Y. enterocolitica in healthy and iron overloaded hosts. In Aim 1, we will determine the susceptibility of two distinct hereditary hemochromatosis mouse models to infection with Y. pseudotuberculosis and Y. enterocolitica, correlating bacterial replication with tissue iron content and production of inflammatory mediators. In Aim 2, we will determine the Y. pseudotuberculosis protein and RNA genes controlled by changes in iron availability as well as genes controlled by IscR. In addition, the impact of IscR on Y. pseudotuberculosis virulence in healthy and iron overloaded hosts will be determined using the hereditary hemochromatosis mouse models. At the conclusion of this study, we will have established several parameters controlling Yersinia infection in iron overloaded hosts, determined the identity of important Yersinia genes controlled by changes in iron availability, completed initial characterization of th previously-unstudied Yersinia IscR gene, and developed important new tools for further investigating Yersinia pathogenesis and iron overload.